Mick,
Under the conditions specified by the OP you do want Hard disk first, then
DVD.
Because the hard disk at present does not have a boot sector, the first
stage will fall to booting from the DVD. the Vista DVD will partion, format,
place boot sector on the hard disk, then transfer its files to the hard disk
and perform a reboot. This second time will find the boot sector and boot
from the harddisk, the installation will proceed from there.
If you set it up DVD first, then harddisk when it comes time for the second
phase the OP must remember to remove the DVD from the drive or it will boot
from there again rather than the hard drive (Instruction to the user do say
remove the DVD but who pays attention the first time
).
After Vista is setup you can no longer boot from the DVD (a good thing) till
you do set the boot sequence to DVD then Hard disk as you note. If you leave
it as DVD -> Hard disk then boot time will be sightly increased as it tries
to find a boot sector on the DVD. If you leave it hard disk -> DVD and the
hard drive again becomes unbootable the OP can again boot from the DVD for
maintenance without reverting to BIOS changes again.
Normally I would agree that DVD -> hard drive is necessary for upgrading a
system with a functioning hard drive boot sector, this case was a bit
special in that it was a brand new hard drive without a boot sector.
Michael